1. Field of Invention
This invention relates to the field of electrical engineering/electrical circuits. Specifically, this electrical circuit is intended to be used in larger circuits. Performance issues, cost issues, part availability issues, as well as other factors make this circuit expressly desirable as a replacement for passive rectifier alternatives in certain applications.
2. Prior Art
The first device used for rectification of current was the vacuum tube rectifier. This included a heated cathode, a heating wire, and an anode. The electrons on the cathode would gain sufficient energy from the heater that they would break free of the cathode and would head toward the anode. Electrons that collected at the anode, though, would not have sufficient energy to leave, and hence would be stuck at the anode. In this way, electrical current would flow in only one direction.
After the hollow state rectifier, the solid state p-n junction rectifier was used for controlling the direction of electricity in electrical circuits. FIG. 3 shows a graph of an actual p-n junction showing resistance vs. forward biased voltage on the junction. As the voltage increases, the resistance on the junction decreases. The two main features that are important on this diagram are the existence of a voltage where the device begins to turn on, called the knee voltage, and also the average slope of the tangent line to characteristic line within the knee region. The knee voltage in a semiconductor is intrinsic to the semi-conductive material being used while the shape of the knee region varies. Little adjustment is possible even at the silicon foundry. This is not a problem for power rectification of AC waves to DC voltage, for power regulation using non-precision voltage references like zener diodes, or for comparison of voltages where the signal is significant. When higher precision is necessary, having control of additional variables can make design of larger electrical circuits easier. Additionally, in instances where cheap, high current, low resistance active devices are available, it may be cheaper to use an active high power device rather than a high power passive rectifier. The flexibility to substitute a power circuit utilizing an active rectifier in place of a high power solid state rectifier allows additional flexibility by designers in what is becoming a highly competitive field. In the area of power rectification, the power component is by far the most expensive part, and its substitution has the greatest capability of decreased cost and increased profit. Even in low power applications, the additional flexibility allowed by changing the characteristic curves make this circuit valuable.
3. Objects and Advantages
This circuit takes the place of a passive rectifier in applications where:                a) A different knee voltage is desired from the knee voltages available from the different passive diodes, or        b) A different slope on the knee is desired than available from commonly available diodes, or        c) There is a need to dissipate lower total wattage than with a conventional passive rectifier.        For example, a FETs (Field Effect Transistor, a common switching device) typically generate substantially less heat and are more power efficient than their passive junction cousins. It is actually possible to use parts which cause this active rectifier to dissipate lower wattage overall than any diode commonly available.        d) Accomplishes rectification like a solid state rectifier utilizing a different power component allowing for additional flexibility in manufacturing power circuits based on economic conditions.        e) Additional variables including speed of switch, slope, thermal dissipation, etc. are required that would either be impossible to obtain using stock passive parts, or would cost more.        
Of noticeable importance is that this invention is capable of having lower knee voltages than any power diode presently in production or having, conversely, higher knee voltages than any diode presently in production. Beyond these benefits, the active rectifier circuit can also dissipate lower wattage than the passive cousins which gives many reasons to spend the extra effort to build this active circuit with substantially more parts. Also note, however, that these are not the only advantages of this invention. This invention has at least two degrees of flexibility over the passive alternative. Hence, for any application where the passive solution doesn't quite meet the requirements, the active rectifier may.
Additionally, as mentioned above, being able to accomplish an old task in an alternative way opens new avenues depending on economics and part availability. In a condition where there is high demand for high power transistors, the price for parts may be sufficiently lower than traditional power rectifiers so that utilization of the active rectifier as a replacement may in the future prove useful to reduce price. If that is not the case, then other issues including availability, temperature ranges, integration, etc. could also prove an obstacle where a manufacturer may prefer to use this complex circuit over the conventional solid state high power PN junction.